NSNib

Instances of the NSNib class serve as object wrappers, or containers, for Interface Builder nib files. An NSNib object keeps the contents of a nib file resident in memory, ready for unarchiving and instantiation.

When you create an NSNib object using the contents of a nib file, the object loads the contents of the referenced nib bundle—the object graph as well as any images and sounds—into memory; but it does not yet unarchive it. To unarchive all of the nib data and thus truly instantiate the nib you must call one of the instantiate... methods of NSNib.

During the instantiation process, each object in the archive is unarchived and then initialized using the method befitting its type. View classes are initialized using their initWithFrame: method. Custom objects are initialized using their init method. In the case of Cocoa views (and custom views that have options on an associated Interface Builder palette) the initialization process also reads in any values set by the user in Interface Builder.

Once all objects have been instantiated and initialized from the archive, the nib loading code attempts to reestablish the connections between each object’s outlets and the corresponding target objects. If your custom objects have outlets, the NSNib object attempts to reestablish any connections you created in Interface Builder. It starts by trying to establish the connections using your object’s own methods first. For each outlet that needs a connection, the NSNib object looks for a method of the form setOutletName: in your object. If that method exists, the nib object calls it, passing the target object as a parameter. If you did not define a setter method with that exact name, the NSNib object searches the object for an instance variable (of type IBOutlet id) with the corresponding outlet name and tries to set its value directly. If an instance variable with the correct name cannot be found, initialization of that connection does not occur.

After all objects have been initialized and their connections reestablished, each object receives an awakeFromNib message. You can override this method in your custom objects to perform any additional initialization.

Subclassing Notes

You can subclass NSNib if you want to extend or specialize nib-loading behavior. For example, you could create a custom NSNib subclass that performs some post-processing on the top-level objects returned from the instantiateNib... methods. If you want to modify how nib instantiations are performed, it is recommended that you override the primitive method instantiateWithOwner:topLevelObjects:. Note that the instance variables of NSNib are private and thus are not available to subclasses. Any override of initWithNibData:bundle: or initWithNibNamed:bundle: should first invoke the superclass implementation.

Deprecation Statement

Declaration

Parameters

nibFileURL

The location of the nib file.

Return Value

The initialized NSNib object or nil if there were errors during initialization or the nib file could not be located.

Discussion

When you instantiate the nib objects later, the NSNib object looks for an appropriate bundle from which to search for any additional resources referenced by the nib. Because you do not specify a bundle directory when calling this method, the receiver uses the bundle associated with the class of the nib file’s owner. If the nib file does not have an owner, the receiver uses the application’s main bundle instead.

Declaration

Parameters

The name of the nib file, without any leading path information. Inclusion of the .nib extension on the nib file name is optional.

bundle

The bundle in which to search for the nib file. If you specify nil, this method looks for the nib file in the main bundle.

Return Value

The initialized NSNib object or nil if there were errors during initialization or the nib file could not be located.

Discussion

The NSNib object looks for the nib file in the bundle's language-specific project directories first, followed by the Resources directory.

After the nib file has been loaded, the NSNib object uses the bundle’s resource map to locate additional resources referenced by the nib. If you specified nil for the bundle parameter, the NSNib object looks for those resources in the bundle associated with the class of the nib file’s owner instead. If the nib file does not have an owner, the NSNib object looks for additional resources in the application’s main bundle.

Deprecation Statement

Declaration

Parameters

owner

The object to use as the owner of the nib file. If the nib file has an owner, you must specify a valid object for this parameter.

topLevelObjects

On input, a variable capable of holding an NSArray object. On output, this variable contains an autoreleased NSArray object containing the top-level objects from the nib file. You may specify nil for this parameter if you are not interested in the top-level objects.

Return Value

Discussion

You may use this method to instantiate a nib file multiple times. This is a convenience method that composes the name-table dictionary and invokes the instantiateNibWithExternalNameTable: method, passing it the name table.

Return Value

Discussion

This is the primitive method for performing instantiations of a nib file. You may use this method to instantiate a nib file multiple times. Each instantiation of the nib must have a distinct owner object that is responsible for the resulting object tree.

If the nib file requires an owner, the externalNameTable parameter must contain the object representing the nib file’s owner (associated with the NSNibOwner key). The parameter may optionally include an NSMutableArray object to be populated with the top-level objects nib file (associated with the NSNibTopLevelObjects key).

Parameters

Return Value

YEStrue if the nib is instantiated; otherwise NOfalse.

Discussion

Unlike legacy methods, the objects adhere to standard Cocoa memory management rules; it is necessary to keep a strong reference to the objects or the array to prevent the nib contents from being deallocated.

Outlets to top level objects should be strong references to demonstrate ownership and prevent deallocation.